1. Field of the Invention
The present invention relates to a high voltage generating device for example for driving a charger in an electrophotographic apparatus.
2. Description of the Prior Art
Conventionally, such a high voltage generating device has a structure as shown in FIG. 1, wherein provided are a conventional high-voltage transformer T; a primary coil W1 thereof; a secondary output coil W2 thereof; a smoothing condenser C; a rectifying diode D; and a spark suppressing resistor R. The output high voltage V2 is equal to the sum of the output voltage V1 of the transformer itself and the voltage V3 of the other coil terminal.
In case of varying the voltage V3 in order to widen the variable range of said high output voltage V2 in such circuit, there is proposed a method of connecting the rectified output of a rectifying circuit RC as shown in FIG. 2 to the terminal of the voltage V3 of the transformer T and to modify the output of said rectifying circuit RC. In such case, however, the potential V3 is inevitably limited within a certain range due to the insulation or other conditions of said terminal or components or patterns relating thereto which are shown in FIG. 2. Also in case the rectifying circuit shown in FIG. 2 is formed, for example, on a printed circuit board, a relatively large circuit structure is inevitable in order to realize a high insulation voltage by a sufficiently large distances between the components.
On the other hand, in case of supplying different plural loads with high voltages, the use of the transformer and control switching element as shown in FIG. 1 for each load leads inevitably to a larger structure and a higher cost. It is therefore desirable to employ a transformer for providing high voltages to plural loads. In such an arrangement, however, independent control of the voltage supply is quite difficult because, in the common use of a transformer for plural loads, the control of a high voltage to be supplied to a load affects the high voltages supplied to other loads.